The Sdk of android 4.0.1(Ics) was publicly release on October 2011.The source of android 4.0 became available on 14th November 2012 3days before the release of Samsung Google nexus.
Android operating system

Other android versions:
v1.1
v1.5                   DONUT
v1.6                   CUPCAKE
V2.0/2.1            ECLAIR
v2.2                    FROYO
v2.34/2.36          GINGERBREAD
v3.0*                  HONEYCOM
v4.0*                  ICS - "LATEST GOOGLE ANDROID VERSION"

Company /developer	Google Inc, Open Handset Alliance
Programmed in	C (core),[1] Java (UI), C++
Working state	Current
Source model	Open Source[2][3]
Initial release	20 September 2008
Latest stable release	4.0.3 (Ice Cream Sandwich) / 16 December 2011; 58 days ago[4]
Package manager	Android Market / APK
Supported platforms	ARM, MIPS,[5] x86 [6][7]
Kernel type	Monolithic (Linux kernel)
Default user interface	Graphical
License	Apache License 2.0 Linux kernel patches under GNU GPL v2[8]
Official website	www.android.com